This invention relates to a multiple needle tufting machine, and more particularly to a needle bar assembly for a multiple needle tufting machine.
The conventional needle bars for multiple needle tufting machines are long, continuous, solid bars extending transversely of the machine above the base fabric for the entire width of the fabric to be tufted. A conventional needle bar includes a plurality of needle holes extending vertically through the needle bar and desirably parallel to each other, uniformly spaced at the desired needle gauge. Each needle is inserted through the needle hole in the bottom of the needle bar so that each needle extends substantially the full height, if not the full height, of the needle bar. The needles are secured in position in their respective needle holes by transverse set screws.
The conventional needle bar has always been one of the most difficult parts of a tufting machine to manufacture, since the numerous needle holes must be drilled very accurately in the long needle bar. It is extremely difficult to control the path of the drill bit through a needle bar which is usually 7/8" in depth or height. In the drilling operation, the drill bit often "leads off" in one direction or another at an angle to the vertical. Accordingly, such angular drill holes through the needle bar will not be parallel to each other. Therefore, the elongated needles extending through the angular needle holes would be "off gauge" where the needle holes are not drilled in truly vertical paths. The longer the needle, therefore, the greater the gauge error.
The "leadoff" of the drilling paths for each needle hole may be caused by various factors. A drill bit which is not accurately ground, or a drill bit being forced too rapidly into the metal of the needle bar, or a drill bit striking the more dense or harder portion of the metal in the needle bar, can cause the drill bit to deflect from its truly vertical course. Once the "leadoff" begins, the continuing path of the drill bit will diverge further away from the desired vertical course.
Once the drilling of the conventional needle bar has commenced, it is not possible to determine the path of the drill bit unitl it emerges from the opposite side of the needle bar. In a multiple needle tufting machine having several hundred needles, the gauge errors between the needles caused by the inaccurate drilling of the needle holes can create considerable problems.
Not only does the drilling of the needle holes involve maintaining accurate control of the drilling paths of the drill bits, but occasionally a drill bit will break off in the drilled needle hole, and the broken drill bit cannot be removed without damaging the needle bar.
All of the above problems in the drilling of the needle holes can result in a needle bar which cannot be used and which must be discarded or scrapped.
Normally, it takes approximately 40 man-hours to drill all of the required needle holes in a conventional needle bar of a multiple needle tufting machine.